One step from oxides to sustainable bulk alloys.

Metallurgical production traditionally involves three steps: extracting metals from ores, mixing them into alloys by liquid processing and thermomechanical processing to achieve the desired microstructures 1,2 . This sequential approach, practised since the Bronze Age, reaches its limit today because of the urgent demand for a sustainable economy 2-5 : almost 10% of all greenhouse gas emissions are because of the use of fossil reductants and high-temperature metallurgical processing. Here we present a H 2 -based redox synthesis and compaction approach that reforms traditional alloy-making by merging metal extraction, alloying and thermomechanical processing into one single solid-state operation. We propose a thermodynamically informed guideline and a general kinetic conception to dissolve the classical boundaries between extractive and physical metallurgy, unlocking tremendous sustainable bulk alloy design opportunities. We exemplify this approach for the case of Fe-Ni invar bulk alloys 6,7 , one of the most appealing ferrous materials but the dirtiest to produce: invar shows uniquely low thermal expansion 6,8,9 , enabling key applications spanning from precision instruments to cryogenic components 10-13 . Yet, it is notoriously eco-unfriendly, with Ni causing more than 10 times higher CO 2 emission than Fe per kilogram production 2,14 , qualifying this alloy class as a perfect demonstrator case. Our sustainable method turns oxides directly into green alloys in bulk forms, with application-worthy properties, all obtained at temperatures far below the bulk melting point, while maintaining a zero CO 2 footprint.